1. Field of the Invention
The present invention relates generally to the operation of a hybrid vehicle, and more particularly to method and system controller for controlling torque matching in a hybrid electric vehicle to limit noise, vibration, and harshness (NVH).
2. Background Art
Hybrid electric vehicles (HEVs) having a primary power source, whether the primary power source is an internal combustion engine or a fuel cell arrangement, typically include a transfer brake and a motor/generator to controllably transfer energy between the primary power source and a secondary electric system.
The transfer brake can be engaged to prevent the motor/generator from producing or receiving torque from the primary power source. The transfer brake is then disengaged to permit the motor/generator to produce or receive torque. It is desirable for the motor/generator torque to match the torque provided by the primary power source when the transfer brake is disengaged. The failure or mismatch of the motor/generator to match the torque of the primary power source can produced noise, vibration and harshness (NVH). In some cases, the NVH can cause erratic acceleration or deceleration, excessive vibration, or other discomforting sensation to be felt by the passengers.
The severity of the NVH is generally related to the degree of torque mismatching. As such, it is desirable to accurately determine the actual torque produced by the primary power source so that the motor/generator can be controlled to produce closely matching torque.
In the past, a torque estimate derived from operating parameters of the primary power source would be used by a vehicle system controller to match the motor/generator torque. One problem with this approach is that the operating parameters used to estimate the torque can and often do include inaccuracies which limit the accuracy of the estimated torque to the actual torque. This inaccuracy can make it difficult to match the motor/generator torque.
Accordingly, there exists a need to provide a more accurate estimate of the torque actually produced by the primary power source that would permit better torque matching during transfer brake disengagement.